Process for making alkenyl benzenes



" been unsatisfactory because the dehydrohalogen- Patented Feblll, 1941 UNITED STATES rnoozss roa Mame museums William M. Qnattlebanm and nourish. at...

Charleston, W. Va. assignors to Carbide and v Carbon Chemicals Corporation, a corporation of New York No Drawing.

Application September 2,1987, s i-a1 No. 162,144

- 6' Claims. (01. zco-sss) This invention relates to a process for making alkenyl benzenes, or styrenes, from halogenated! alkyl benzenes. Specifically, the process provides an improved method for purifying the halogenated-alkyl benzene and removing hydrogen halide therefrom under such conditions that the alkenyl benzene is produced at higher-reaction rates, in purer form, and in greater yields than by any method known heretofore.

The halogenated-alkyl benzenes suitable for the production of styrenes-by this process are those in which a halogen is substituted in the alpha position in a side chain, or alkyl group. These compounds may be prepared by any of the usual methods, although the chloroalkyl and bromoalkyl benzenes are most easily made by the direct halogenation of the. alkyl benzene, vusing the corresponding phosphorus trior pentahalide as a catalyst for confining. the substitution to a side chain.

The-removal of hydrogen halide from halogenated-alkyl benzene is ordinarily accomplished by heating the latter with theoretical or excess quantities of certain bases, such as .qulnoline. pyridine, amines, and the like. All the known processes for the removal of hydrogen halide from the halogenated-alkyl benzene to form styrenes are attended with certain serious'disadvantages. The use of excess or even theoretical amounts of the required bases is almost prohibitive from the commercial standpoint. While the useofaminesoraminesaltsinlessthantheoretical amounts has been suggested, the products heretofore have been impure and the yields low due to the high production of resinous materials. In any case, the production of the styrenes has ation rates of the halogenated-alkyl benzenes,

, obtainable under the above procedures, have been low.

Other disadvantages of the processes employed heretofore are the difllculty of producing pure halogenated-alkyl benzeiies, and rapid corrosion of the metal equipment used in their purification. V

The process of this invention is an'improvement over all processes known or suggested heretofore. It provides a method whereby alkenyl benzenes-may be produced in a pure state at reaction rates far greater than any obtainable heretofore, and which avoids the formation of appreciable amounts of by-products or resinous materials. At the sametime, this process provides 'a method whereby the halogenated-alk'yl benzene may be purified without decomposition, and this purification may be conducted in metal equipment which would otherwise be rapidly corroded.

Since this invention is especially applicable to the production of vinyl benzene, or styrene, by

the removal of hydrogen chloride from chloroethyl benzene, the following description of the process refers specifically thereto, although the process may be applied to the production of other alkenyl benzenes with satisfactory results.

In the production of styrene by this process, it

is highly desirable to purify the chloroethyl benzene prior to removal of hydrogen chloride, for the reason that it isextremely diflicult to separate any ethyl benzene (residual in the crude chloroethyl benzene from the chlorination reaction) from styrene by distillation. The chloroethyl benzene itself decomposestosome extent upon distillation under ordinary conditions, with evolution of hydrogen chloride. This may be prevented by adding to the crude chloroethyl benzene a smml amount of a stabilizing or decomposition-preventing agent. Ammonia,

amines and amine salts have been found particularly useful for this purpose. For instance, the addition of as little as 0.1% of dioctyl amine or of triethanolamine has been found to stabilize .the chloroethyl benzene, and the latter may then be distilled without decomposition, preferablyat an absolutepressure below 30 mm. of mercury.

Moreover, the product thus stabilized may be distilled in metal equipment which would other-= wise be badly corroded. Copper and alloys of high copper content have proven especially satisfactory when ammonia is used as .the stabilizer.

' The pure chloroethyl benzene, obtained by the above procedure, is dehydrochlorinated by'heating in the presence of an amine or amine salt at a temperature preferably from about to about 350 C. The exact temperature of operation will" depend upon the particular circumstances of, operation. The dehydrochlorination of the chloroethyl benzene may be conducted entirely in the vapor phase, 'or it may becarried out in the liquid phase by heating chloroethyl benzene containing substantial quantities of dissolved an iine salt, or by heating an amine salt in whichis maintained at least 1%, and preferably 5% to 10%, of dissolved chloroethyl benzene.

"Ihis application is directed specifically to the process in which the reaction is conducted in liquid phase. The process in whichthe reaction is conducted'in vapor phase is the subject of our copending application Serial No. 365,567 filed November 14," 1940.

If the reaction is conducted in the vapor phase,

. the chloroethyl benzene containing about 1.0% of 5 an amine, such as dioctyl amine, or an amine salt, such as dioctyl amine hydrochloride, may

be conveniently passed through a chamber or seriesof tubes maintained at a temperature of about 300 to 350 C.

- When operating in the liquid phase, using chloroethyl benzene containing dissolved amine salt, the mixture may be heated at about 140 to 190 /'C., removing continuously the styrene formed. Although as little as 1%. of the soluble catalyst may be used, improved rates and yields are ob- 'tained as the quantity of catalyst is increased,

until finally catalyst concentrations of 90% to 97% the maximum rates and highest yields are obtained.

The preferred procedure, giving the highest rate of dehydrohalogenation, consists in introducing chloroethyl benzene into a molten higher amine salt, and removing the styrene as fast as formed; the proper ratio of catalyst to chloroethyl benzene is maintained, as indicated by the hundred times as fast as by any methods known heretofore.

Amines suitable for use in this process are those. which yield salts which are stable at the temperatures used for the dehydrohalogenation reaction, and in which the halogenated-alkyi ben- 40 zene will dissolve. The following amines and their salts have been used most successfully in this reaction: di-2-ethylhexyl amine, diamylamine, triamylamine, dioctylethylamine, dioctyl: benzylamine and di-2-ethyibutylamine. The preferred catalyst is di-2-ethylhexylamine hydrochloride. These catalysts will dehydrohalogenate about to 100 times their own weight of chloro- .ethyl benzene before decreasing substantially in activity. They may be recovered by distillation 50 under reduced pressure, or by neutralizing the spent catalyst with alkali and distilling the free The process of this invention. will be illustrated by the following examplw:

' Example 1 Anhydrous ethyl benzene was placed in a container provided with a gas inlet tube extending to its" bottom, a stirrer, and a reflux condenser. About. 1% by weight of phosphorus pentachlorlde was addedtothe ethyl benzene, and the mixture was-brought .to a temperature of about C.

This temperature was maintained throughout the chlorination reaction. The contents of the ficontainer'werestirred vigorously, and chlorine was introduced 'at a rapid rate by means of the as inlettube until-about 60% of the theoretical amount of chlorine had been absorbed. Dissolved hydrogen chloride and excess chlorine e e h absolute 30 mm; of mercury. The.

- fraction boiling'between and 84 C. at an obsolute pressure of 20 of mercury was col-- lected. If the crude chlorinated material was to be distilled in copper equipment it was treated with anhydrous ammonia instead of with dioctyl amine, since the latter tends to corrode copper. I

Example 2 The dehydrochiorination of the chloroethyl benzene, prepared in Example 1, was carried out by placing about 100 parts byweight of dioctyl l0 amine in a container provided with a thermometer, dropping funnel, and a fractionating column with updraft condenser arranged for partial return of the distillate. The amine was heated to about 240 C. and a continuous stream of chlorol5 ethyl benzene was introduced-into it. The rate was carefully controlled to avoid lowering the temperature of the catalyst, and building up an excess f chloroethyl benzenein the container. 1 Styrene began to distil immediately and the hy- 20 drochloride'of dioctyl amine was soon formed. When this had occurred, dry hydrogen chloride was evolved along with the styrene and removed at the top of the condenser. Styrene was removed as fast as it was formed, and a small 25 amount was purposely returned as reflux to keep the temperature of the distillate below 140 C. The distillate contained about 85% to about styrene, the remainder being chloroethyl benzene. A single distillation of this mixture gave styrene .30 in a state of high purity, boiling at 46 C. at an absolute pressure of 20 mm. of mercury. The

I residue from this reaction was about 0.5% of the total through-put of choloroethyl benzene. The reaction rat-e was about 8 times the container 5 charge per hour.

Although the invention has been described in detail in connection with the production of styrene from chloroethyl benzene, it may also be employed for the production of other alkenyl benzenes. For example, diethyl benzene may be chlorinated and treatedto produce divinyl benzene, and bromine may replace the chlorine in the process.

Other amines or salts of amines may be used 45 both as stabilizers and catalysts, but, in general, higher aliphatic amines or amine salts are preferred. The quantities of amines or salts used both .as stabilizers and catalysts may be varied considerably, but as stabilizers and for complete 50 vapor phase dehydrohalogenation of the halogenated-alkyl, benzene, amounts of about 0.1% to 1.0% of the amines or salts are preferred.

Materials commonly used for reaction equipment may be considered more or less unsatisfac- 55 tory for dehydrochlorination due to corrosion during the process. The higher reaction rates obtained with the processes of the present invention warrant ,the use of more costly material's than the slower processes of the prior art. Mo-

lybdenum'and tantalum have been found tohave low corrosion rates.

The foregoing description is given by way of iilustration, and many modifications of the process may be made within the scope of the invention as defined by the appended claims.- We claim:

1. In the process of preparing an alkenyl benzeneby the dehydrohalogenation of an alpha more than four carbon atoms, said salt being miscible with the halogenated alkyl benzene at the temperature of operation; passing the halogenated alkyl benzene into said molten catalyst at a rate such that at all times the concentration of the amine saltinthe reaction mixture is at least about 90%; and removing the alkenyl benzene erefrom in the vapor phase as it is formed,

2. In the process of preparing styrene by the dehy irochlorination of alpha chlorethyl benzene, the step of producing thestyrene at a high rate of reaction and with a minimum formation of byproducts and resinous materials, which comprises maintaining va molten catalyst at a temperature from about 150 to about 300? (1., said catalyst comprising a stable amine salt which is miscible with the chlorethyl benzene at the temperature of operation; passing the chlorethyl benzene into said molten catalyst at a rate. such that at all times the concentration of the amine salt in the reaction mixture is at least about and removing the styrene therefrom in the vapor phase as itis formed. 4 c x 3. In the process of preparing styrene by the dehydrochlorination of alpha chlorethyl benzene, the step of producing the styrene at a high rate of reaction and with a minimum formation of byproducts and resinous materials, which comprises maintaining a molten catalyst at a, temperature from about to about 300 0., said catalyst mmprising a stable salt of an amine having at least two substituent organic radicles each of which contains more an four ,carbon atoms, said salt being miscible with chlorethyl benzene at the temperature'of operation; passing the chlorethyl benzene into said molten catalyst at a rate such that at all times the concentration of the amine salt in the reaction mixture is, at least about 90%; and removing the styrene therefrom in" the vapor phase as it is formed.

4. In the process of preparing styrene .dehydrochiorination of alpha chlorethyl benzene.

the step of producing the styrene at a high rate of reaction and with a minimum formation of byproducts and resinous materials, which comprises maintaining a molten catalyst at a temperature from about 150 to about 300 0., said catalyst comprising a stable salt of dloctyl amine which is miscible with the chlorethyl benzene at the temperature of' operation; passing the chlorethyl benzene into said molten catalyst at a rate such that at all times the concentration of the aminesalt in the reaction mixture is at least about 90%; and removing the styrene therefrom in the vapor phaseas it is formed.

5. In the process of preparing styrene by the dehydrochlorination of alpha chlorethyl benzene,

the step of producing the styrene at a high rate of reaction and with a minimum formation of byproducts and resinous materialsrwhich comprises maintaining a molten catalyst at a temperature from about 150 to about 300 0., said catalyst comprising a stable salt of triamyl amine which is miscible with the chlorethyl benzene at the temperature of operation; passing the chlorethyl benzene into said molten catalyst at a-rate such that at all-times the concentration of the amine' salt in the reaction mixture is at least about 90% and removing the styrene therefrom in the vapor phase as it is formed.

6. In the process of preparing styrene by the dehydrochlorination of alpha chlorethyl benzene, the step of producing the styrene at a high rate of reaction and with a minimum formation of byproducts and resinous materials, which comprises maintaining a molten catalyst at a temperature from 'about 150 to-about 300 C., said catalyst comprising a stable salt of dioctylethyl amine which is miscible with the chlorethyl benzene at the temperature of operation: passing the chlorethyl benzene into said molten catalyst at a rate such that at all times the concentration of the amine salt in the reaction mixture is at least about 90%: and removing the styrene therefrom in'the vapor phase asit is formed.

. WILLIAM M. QUA'I'ILEBAUM. DONALD M. YOUNG. 

